So, silica gel: not really a gel then?
No, silica gel isn’t a gel like a hair gel. It is a solid material that comes in granular or beaded forms. These granules or beads are sorted according to their size.
But does silica gel get wet as it adsorbs water?
No it doesn’t, it traps water molecules inside its pores yet remains dry and appears physically unchanged.
Silica gel is a desiccant then?
Yes, it adsorbs water vapour by physical means, not a chemical reaction. Water vapour is attracted inside the silica gels crystalline structure.
…and it changes colour as it adsorbs moisture?
The basic white non-indicating silica gel doesn’t. But self-indicating silica gels do. They are impregnated with moisture sensitive indicators which change colour as they adsorb moisture. For example, an orange silica gel which changes to dark green as it adsorbs moisture. The purpose of this being to indicate when the silica gel is saturated and unable to take up any more moisture (orange = dry, dark green = near exhausted in this case).
Does silica gel comes ready to use?
Yes. The silica gel does not need to be ‘generated’ before use. It is always sold (loose or in sachets) in a dry condition, ready for use.
How long can silica gel be usefully stored?
The shelf life of silica gel is between 4 and 12 months (although practical experience has shown that it can often far exceed this). The crucial factor is to keep it in a sealed environment until it is needed for use – it will, of course, adsorb moisture from any environment. Although the moisture uptake rate is not fast, small sachets can be particularly vulnerable to poor storage conditions – it is recommended that they are not left open to the atmosphere for longer than 15 minutes.
How much water vapour can silica gel hold?
Silica gel will adsorb up to 40% of its’ own weight in moisture.
Can silica gel be used anywhere?
Theoretically yes, but it is really only effective in an enclosed environment. In a situation where new air (and moisture) is constantly being introduced, an unpractical amount of silica gel will likely be needed to keep the Relative Humidity at low levels.